TIG welding

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Tungsten inert gas (TIG) welding, also known as gas tungsten arc welding (GTAW), and Heliarc is a type of arc welding in which a non-consumable tungsten electrode is used to join metals. An inert gas, most commonly argon, is used to shield the weld pool from contaminants, resulting in a clean, strong weld joint. This shielding gas prevents oxidation of the tungsten electrode, the molten weld puddle and the heat-affected zone adjacent to the weld bead.

Shielding Gases

TIG welding utilizes inert gas to shield the welding arc and hot metals. The atomic structures of inert gases prevent them from reacting with metals or other gases. Argon, helium or argon-helium mixtures are used as inert gases in TIG welding.

Argon

Argon, a relatively heavy gas, has several benefits when used in TIG welding.

It requires a lower arc voltage than other shielding gases for a given arc length and current (ideal for welding thin metals).
It provides easier arc starting than other gases.
Its heavier weight (compared to helium) provides for good shielding with lower flow rates.

Helium

Helium is the lightest of the inert gases. Due to its light weight, approximately two to three times more helium is needed to shield a weld area than argon. However, helium can be used with greater arc voltages than argon, which is why helium is preferred when working with thick metal sections.

Proper Gas Selection

Another difference between helium and argon is cleaning ability. Both helium and argon allow for good cleaning action when using DC. However, when using AC, argon provides better cleaning action. Argon also provides better arc stability than helium when using AC. Proper gas selection is important. Pure argon is used most frequently, but a mixture of helium and argon or other specialty mixes may be appropriate for welding thicker metals. Inappropriate gas mixtures may result in an electrode being consumed or deposited in the weld puddle too quickly.

GTAW setup

Equipment

In a typical TIG setup, an AC/DC welding machine is used with a flow of shielding gas. The shielding gas goes through a regulator and flow meter, then on to the torch. The torch has a collet/collet body combination that holds the electrode. A heat-resistant cup or ceramic nozzle surrounds the electrode and controls the gas shield. Air-cooled torches are adequate for welding at 200 amps or less, whereas water-cooled torches should be considered when welding above 200 amps. Foot pedal controls and torch controls are available for TIG welding. Foot pedal controls are popular in work areas affording mobility, while fingertip controls can be beneficial when working in awkward positions or when less mobility is available.

When it comes to major industrial construction the equipment used is typically a Stick welding power supply with a TIG torch attached to the stinger. The TIG torch is nothing more than an air cooled torch with no controls except a valve to turn on the gas. In this case the arc is established by scratch starting.^[1]

Safety Precautions

Although TIG welding does not produce the metal spatter common to arc welding or stick welding welding, it does generate intense heat and light. In fact, the clearer atmosphere around the TIG arc can cause up to twice the amount of infrared and UV rays produced by normal arc welding. Any exposed skin will be experience damage similar to extreme sunburn. Welders must wear a welding helmet, and protective gloves and clothing should also be used. Fire-resistant cloth and leather clothing and accessories are recommended. Cotton is not advised, as it does not provide sufficient protection and deteriorates quickly under the infrared and UV rays produced by the welding process. Finally, dark clothing should be worn to reduce reflection of light behind the helmet.^[2]